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Discussion Starter · #1 ·
Hey there y’all, having an EGR issue at the moment and looking for someone’s thoughts on it. I recently cut my muffler off and everything downstream from the high flow cat, because I was redoing it. I was driving it to work no issue and then at about 40 miles or so it starts to (what sounded like) misfiring. Rpm’s surging at idle, running very rich, loss of power… the whole ordeal haha. I drove a mile home and CEL came on, and had a IAT sensor issue. It was just unplugged, so I plugged it in cleared the codes and worked for another 40 miles. Now I’m getting an EGR code po402. I just cleaned the egr valve and no luck, though it was very dirty with carbon. My next thought is a lack of backpressure causing sensors to be thrown off based on the stock ECU sensor specs. Would this lack of back pressure cause this or what’s anyones thoughts? Thanks!
 

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Discussion Starter · #2 ·
Hey there y’all, having an EGR issue at the moment and looking for someone’s thoughts on it. I recently cut my muffler off and everything downstream from the high flow cat, because I was redoing it. I was driving it to work no issue and then at about 40 miles or so it starts to (what sounded like) misfiring. Rpm’s surging at idle, running very rich, loss of power… the whole ordeal haha. I drove a mile home and CEL came on, and had a IAT sensor issue. It was just unplugged, so I plugged it in cleared the codes and worked for another 40 miles. Now I’m getting an EGR code po402. I just cleaned the egr valve and no luck, though it was very dirty with carbon. My next thought is a lack of backpressure causing sensors to be thrown off based on the stock ECU sensor specs. Would this lack of back pressure cause this or what’s anyones thoughts? Thanks!
Just wanted to add it sounds basically cammed and the engines suspiciously vibrating at idle so maybe a misfire triggered that egr code because of almost no backpressure?
 

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Discussion Starter · #4 ·
So just to clarify, are you driving around with your exhaust cut off??
Correct, I’ve been busy with work and haven’t been able to finish the exhaust. It’s dumping right out of my high flow cat. Has a flex pipe attached going off to the side a little but that’s about it.
 

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Discussion Starter · #6 ·
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I could see there being issues caused by having it cut off like this, just by the o2 sensors possibly reading too much oxygen, and that could be messing with the fuel curves. Given I'm not an expert of the newer Broncos and multiple o2's of the 96, but aren't there post cat o2's on the 96??? I had bought my 96 new, so it had no issues when I had it, but the 86 I'm restoring now gave me all kinds of fits from the o2 sensor (single) being messed up, and the wiring being corroded & not getting a signal back to the computer.

I'd say get that exhaust back together and re-evaluate, until then you've introduced too much unknown into the system to possibly diognose anything properly. That may be all it is, but get the exhaust back on and report back.
Great advice, thanks. I have a post cat o2 sensor that has been fine with the exhaust on. Now that it’s off it could be giving bad readings. I have a new chambered Flowmaster that I’ll put on and see how that goes, as well as the rest of the exhaust.
 

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Discussion Starter · #8 ·
Yeah no problem, we're all just figuring it out as we go, im sure your ears will thank you once the exhaust has a muffler again, just be sure to put all the o2's back on in roughly the same areas they were when stock. Then you can pull codes again if its running funny, but something tells me it's just a bit confused on what to do with the downstream o2's off.
Yeah I haven’t touched the sensors since I put the high flow on and haven’t had an issue. When I cut the exhaust off I didn’t touch that sensor at all. Just cut off where the muffler attaches to the cat and put that flex pipe on. So if that sensors confused possibly it’s compensating by giving the injectors too much fuel causing it to bog and maybe give that po402 egr code.
 
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